This invention relates to a method for grinding surfaces of workpieces using a metal bonded grinding wheel, which is sharpened through an electrochemical conditioning by means of an electrode, which is disposed spaced apart from the grinding wheel so that a gap is formed between the electrode and the grinding wheel, an electrolytic cooling lubricant, introduced into said gap, and a power source, by means of which a current is conducted through the electrode, through the electrolytic cooling lubricant and through the grinding wheel.
In addition, the invention relates to a grinding apparatus for surfaces of workpieces with a metal bonded grinding wheel, which can be sharpened through an electrochemical conditioning.
Growing demands with respect to economic efficiency, obtainable workpiece surface quality and precision are being put on grinding methods of this kind, in particular for grinding indexable inserts. Since the respective workpieces are made of very hard material, this means that conventional grinding wheels are no longer able to meet these demands sufficiently. Conventional grinding wheels of this kind have a bonding system of artificial resin or ceramic, by means of which the grinding grains are held. Grinding wheels of this kind have to be sharpened again through a dressing operation after being used for only a short time. Owing to the strong abrasion of the grinding wheel and the relatively frequent dressing operation, the aforementioned demands cannot be fulfilled.
Metal bonded grinding wheels are better suited for grinding methods of this kind. Compared with grinding wheels having other types of bonding, these grinding wheels have great advantages, evidenced in particular by the very high grain retention of the bonding, an enlarged grain protruding length of 30 to 50% of the grain diameter, a larger chip space and a more abrasion-resistant bonding system. Moreover the heat elimination is also optimal, owing to the metallic bonding material.
This metal bonding, however, also has a big drawback. Because of the increased abrasion resistance of the bonding system, the self-sharpening effect is disturbed. The metal bonding of the grinding wheel can no longer be restored through abrasion of the worn material particles. The dull grinding particles are no longer released from the grinding wheel bonding, the whole grinding wheel becomes blunt, and the grinding process very soon comes to a standstill. Restoration of the optimal grinding wheel topography has to take place through a sharpening process, which has as a consequence high non-productive times, and which therefore reduces the economic efficiency of the entire grinding process.
Known from the European patent EP-A-0 576 937 is a method and a device for grinding a mirror surface with a grinding wheel, which grinding wheel has a metal bonding. Here the grinding wheel is sharpened during the grinding operation in that a current is conducted between an electrode, disposed adjacent to the grinding surface of the grinding wheel and the grinding wheel, so that the grinding wheel can be sharpened electrolytically with the aid of a conductive solution.
With this device and method the quality of the surface of the grinding wheel is improved during the operation of grinding the mirror surface; however, it cannot be ascertained whether the grinding wheel would be sharpened more than the grinding operation would require. This could lead to excessive wear and tear on the grinding wheel. It is also not discernible whether the grinding wheel is in a state allowing it to perform an optimal grinding operation.
At the same time, achieving mirror surface quality is only possible by depositing solid lubricants in the form of oxides, hydroxides and cooling lubrication materials in the chip space of the grinding wheel. The chip space of the grinding wheel is thereby greatly reduced in size, whereby the transport of cooling lubricant into the grinding contact zone and material particles out of the grinding contact zone is only possible in a more limited way. Cool-lubricating, abrasion-intensive grinding processes, characterized by very low process forces and stable sharpness conditions over a very long time period, cannot be achieved with the device and the method according to EP-A-0 576 937.